a) Field of the Invention
The present invention relates to low dielectric constant (low k) polymer compositions and more particularly to the use of polycarbosilane materials to enhance the adhesion of low k polymer coatings to adjacent substrates.
b) Related Art
In the prior art fabrication of semiconductor integrated circuit devices, fine patterns of circuitry in the form of semiconductor regions, electrodes, wiring and other components are fabricated onto a semiconductor substrate by using conventional processing, such as etch and chemical vapor deposition (CVD) processes, among others. After formation of a wire pattern on the substrate layer, an interline dielectric material deposition process ensues to both fill in the spaces between the horizontally disposed wiring and overcoat the pattern. Alternatively, a damascene technique can be performed in which a dielectric layer is deposited onto a substrate, patterned, and etched back to create recessed regions in which metal is inlaid to create interconnect wiring. These deposition steps as well as other multi-layer formation processes, well-known in the art, are provided to form a multi-layered integrated semiconductor device.
As the electronics fabrication industry moves towards more compact circuitry with finer circuit or line geometry in densely-packed circuit patterns, the dielectric constant requirements of the insulating layers grows more demanding for lower values. Under these circumstances, the use of low k polymer dielectrics that minimize capacitance and reduce power consumption and cross talk, while increasing signal propagation speed, becomes a necessity. The dielectric materials must possess dielectric constants no higher than 3.0 and should have dielectric constants as low as possible toward a theoretical limit of 1.0. The practical expectation for polymer dielectrics is in the range of 2.2 to 3.0. For organic dielectrics, thermal stability is an important consideration, as semiconductor processing can involve exposure to temperatures in excess of 400xc2x0 C. The organic dielectrics must have glass transition temperatures above 300xc2x0 C. and as high as possible towards 450xc2x0 C., as well as a decomposition temperature in excess of 450xc2x0 C. Preferably, the organic polymers should be easily processed by standard spin-bake-cure processing techniques. The organic dielectrics should also be free from moisture and out-gassing problems, in addition to having expected adhesive and gap-filling qualities, and dimensional stability towards thermal cycling, etching, and chemical mechanical polishing.
Various polymers have been proposed and utilized as dielectric materials for integrated circuits, such polymers including polyimides, and arylene ether polymers. Polyimide resins generally demonstrate high moisture absorption due to their polarizing chemical structures, resulting in an increasing dielectric constant. Organosilicon polymers have also been identified as low dielectric constant materials. In particular, siloxane based resins including hydridosiloxane resins, organohydridosiloxane resins, and spin-on glass siloxanes and silsesquioxanes are used as dielectric layers. Other classes of organosilicon materials include polyperhydrido-silazanes and nanoporous dielectric silica coatings formed from liquid alkoxysilane compositions. Most of these materials exhibit difficulties in processing due to chemical or mechanical instability.
Arylene ether polymers have been found particularly useful as low k dielectric materials in IC applications. Arylene ether polymers have been identified as organic dielectric materials and include poly (arylene ether) (PAE), poly (arylene ether ether ketone) (PAEEK), poly (arylene ether ether acetylene) (PAEEA), poly (arylene ether ether acetylene ether ether ketone) (PAEEAEEK), poly (arylene ether ether acetylene ketone) (PAEEAK), and poly (naphthylene ether) (PNE) comprising different polymer designs that include homopolymers, block or random copolymers, polymer blends, interpenetrating polymer networks (IPNs), and semi-interpenetrating polymer networks (SIPNs). Other examples of organic dielectric materials in current use include the polymeric material obtained from the phenylethynylated aromatic monomer provided by Dow Chemical Company under the trademark SILK(trademark) and the poly (arylene ether) provided by Schumacher under the tradename VELOX(trademark).
In commonly assigned U.S. patent applications Ser. No. 08/665,189, filed on Jun. 14, 1996, and Ser. No. 09/197,478, filed on Dec. 12, 1997, there are disclosed certain poly(arylene ethers) which have low dielectric constants, high glass transition (Tg) temperatures, good thermal stability to and above the Tg, low moisture absorption rate, and good storage modulus retention. However, adhesion of these and the other cited organic polymer insulators to substrate surfaces have been found in need of enhancement, generally requiring addition (or primer application) of known adhesion promoters. These prior art adhesion promoters have been found generally unacceptable in combination with the dielectric poly(arylene ethers) and other organic dielectrics because: (1) their primer application generally requires a separate coating process step; and (2) their presence may generate unanticipated chemical side reactions (e.g. generation of volitiles due to materials breakdown) during IC high temperature processing.
It has presently been discovered that certain polycarbosilanes can be used as compatible a adhesion promoters for low dielectric constant polymers, particularly poly(arylene ethers), and can be used as an additive with these polymers and processed to form modified low k dielectric polymeric coating compositions with enhanced adhesive characteristics. More precisely, it has been found that the adhesion of poly(arylene ether) dielectric coating compositions is particularly enhanced by the primer application or compositional addition of an adhesion promoter material comprising at least one polycarbosilane. The instant polycarbosilane adhesion promoters can be employed as a surface deposition treatment (primer) or as an internal compositional additive to dielectric polymer compositions. These polycarbosilane promoters can be prepared, provided or used at reasonable cost; and provide enduring adhesion to a variety of surfaces.
The present invention provides new and improved adhesion promoting materials effective in enhancing the adhesion of low dielectric constant polymer compositions to various substrates. The new and improved adhesion promoter composition comprises a polycarbosilane of the formula: 
in which:
R1, R7, and R10 each independently represents a substituted or unsubstituted alkylene, cycloalkylene, or arylene group;
R2, R3, R4, R5, R8 and R9 each independently represents a hydrogen atom or organic group.
R6 represents an organosilicon, a silanyl, a siloxyl, or an organo group; and
x, y, z and w satisfying the conditions of [4xe2x89xa6x+y+z+wxe2x89xa6100,000], and y and z and w can collectively or independently be zero.
In order to improve the adhesion of low dielectric constant polymer coatings to electronic surfaces, substrates such as silicon, silicon dioxide, silicon nitride and aluminum are treated with the instant polycarbosilanes as adhesion promoters in two different forms. The polycarbosilane materials can be added to surfaces as primer coatings from a solution containing typically from about 0.05 to 20% by weight of the polycarbosilane promoter. Alternatively and preferably, the polycarbosilane adhesion promoters can be compositionally added to a low k dielectric polymer in certain concentrations and effect in-situ adhesion capability in the cured or dried polymer coating composition. When used as surface primers, the present polycarbosilane adhesion promoter compounds engender superior bonding capacity to substrate surfaces to which low k polymer coatings are subsequently applied. In more preferred embodiments, the polycarbosilane adhesion promoter compounds are added to dielectric polymer compositions and subjected to a thermal or high energy-source to generate coatings having superior adhesion characteristics throughout the entire polymer composition so as to ensure affinity to any contacted surface of the polymer coating. The instant polycarbosilane additives are compatible with low k dielectric polymers thereby enabling formation of polycarbosilane-modified low k dielectric polymers which possess enhanced adhesive characteristics compared with the base polymer, while maintaining the other beneficial physical and electrical properties.
While poly(arylene ether) and the other dielectric organic coating materials have suitable low k dielectric constants and the thermal stability and high mechanical strength characteristics needed for coating presently miniaturized patterned wiring of semiconductor wafers, these prior art materials have less resistance to delamination than is desirable. It has been found that combining poly(arylene ethers) with small, effective amounts of the present polycarbosilane adhesion promoters, spin coating a surface with same, and subjecting the resulting film to a thermal or high energy curing process results in a polycarbosilane-modified poly(arylene ether) polymer film composition having improved adhesion characteristics over those exhibited by the base poly(arylene ether) base polymer. These films possess a low dielectric constant, high thermal stability, high mechanical strength, and excellent adhesion to electronic substrate surfaces including silicon, silicon nitride, titanium nitride, silicon dioxide, aluminum and tantalum. Because the polycarbosilane is molecularly dispersed, these films demonstrate excellent adhesion to all affixed surfaces including underlying substrates and overlayed capping or masking layers, such as SiO2 and Si3N4 capping layers. The use of these polycarbosilane-modified polymer films eliminates the need for an additional process step in the form of at least one primer coating application to achieve adhesion of the film to a substrate and/or overlaid surface.
In accordance with the invention, new and improved poly(arylene ether) coating compositions exhibiting superior adhesion to electronic substrate surfaces are provided, said poly (arylene ether) compositions comprising:
(a) a poly(arylene ether) having the repeating units of the formula:
[xe2x80x94Oxe2x80x94Y1xe2x80x94Oxe2x80x94Ar1xe2x80x94]nxe2x80x94[xe2x80x94Oxe2x80x94Y2xe2x80x94Oxe2x80x94Ar2xe2x80x94]m xe2x80x83xe2x80x83(FORMULA II)
wherein n=0 to 1; and m=1xe2x88x92n; and wherein Y1, Y2, Ar1 and Ar2 are each a divalent arylene radical, Y1 and Y2 being selected from a second group of divalent arylene radicals; and
(b) a small, effective amount of an adhesion promoter comprised of at least one polycarbosilane of Formula (I):
In another aspect of the invention there is provided a method for forming electrically insulating films of the instant polycarbosilane/poly(arylene ether) compositions. This process includes applying a coating of the instant polycarbosilane/poly(arylene ether) adhesion promoting compositions to an electronic substrate surface and subjecting the coating to heat or other high energy to cure the coating thereby forming a thermally stable, adhesive, low dielectric constant (k less than 3.0) polycarbosilane-modified poly(arylene ether) film. This film generating process can employ any form of energy such as thermal (heat) or other high energy such as electron beam (e-beam), U.V. light, and any other functional forms of high energy. These energy sources are applied to the instant polycarbosilane/poly(arylene ether) composition to convert the mixture to low k polycarbosilane-modified poly(arylene ether) film compositions of the present invention. The most expeditious process is the application of thermal energy (heat) to the instant compositions in increasing temperature thermal plateaus of from about 50xc2x0 C. to about 450xc2x0 C. The nature of the subject polycarbosilane/poly(arylene ether) compositions enables use of general wet coating and heating processes in the formation of a very low dielectric constant insulation structures without employing exotic production techniques.
The present invention is also directed to a multilayer electronic circuit article comprising: (i) a silicon, glass or ceramic substrate, (ii) a plurality of layers or regions of an insulating material on a surface of the substrate, and (iii) at least one layer or region of a conductive material selected from the group consisting of metals and semiconductor materials, interposed between adjacent layers of the insulating material or within a layer of the insulating material, the insulating material comprising the low k dielectric polycarbosilane-modified/poly (arylene ether) coatings of the present invention.
When the polycarbosilane/poly(arylene ether) compositions of the instant invention are subjected to an energizing source such as thermal energy, a polycarbosilane-modified poly(arylene ether) low k dielectric film composition is formed. These low k dielectric composition film coatings have the unique feature of good adhesion to a variety of common semiconductor surfaces without the need for any other prior art adhesion enhancing materials, the addition of which would require undesirable additional process steps and carry the risk of decomposition resulting in outgassing of these materials in hostile semiconductor processing environments. The present polycarbosilane-modified poly (arylene ether) coatings have sufficient glass transition temperature values (Tg) above 350xc2x0 C. so as to form heat resistant, low dielectric constant (low k) semiconductor films which withstand harsh high temperature environments in current processing methodology of semiconductor devices.
In addition, the instant dielectric coatings possess good gap filling qualities for integrated circuits in semiconductor articles and therefore completely fill spaces between conductive lines of 0.25 microns (xcexcm) or less. The low k polycarbosilane-modified poly(arylene ether) coatings of the present invention also possess sufficient thermal stability so as not to evidence any out-gassing during ongoing semiconductor processing, low moisture absorption to retain film resistivity, and stability to a variety of common etching and other semiconductor fabrication processes. As in the case of ordinary organic dielectric materials, the present low k polycarbosilane-modified poly(arylene ether) compositions dielectric coatings can be easily applied in high yield to substrates using standard spin-bake-cure processing techniques, thus insuring their cost effectiveness. Finally, the polycarbosilane-modified poly(arylene ether) dielectric coatings developed and disclosed herein are applicable for use in other micro electronic devices in addition to ICs, for example, printed circuit boards (PCBs), multi-chip modules (MCMs) and the like.
The subject invention is based on the finding that certain polycarbosilanes are excellent adhesion promoters and are compatible with poly(arylene ether) compositions. These polycarbosilanes can be compositionally added to the poly(arylene ethers) in small and yet effective amounts to form the adhesive polycarbosilane-modified poly (arylene ether) semiconductor film coatings of the present invention. The polycarbosilane adhesion promoting compounds are added in small, effective amounts of up to 20% based on the weight of the poly(arylene ether) base polymer composition, and amounts up to about 5.0% by weight of the a base polymer are generally preferred. Operable ranges of polycarbosilane are from about 0.5 to 20% while preferred ranges are from about 0.5 to 5% based on the weight of the poly(arylene ether) base polymer.
Preferred adhesion promoting polycarbosilane compounds of the invention are polycarbosilanes in which the R2 group of Formula I is a hydrogen atom or an and R1 is methylene and the appendent radicals w, y, and z are zero. Other preferred adhesion promoting polycarbosilane compounds of the invention are polycarbosilanes of Formula I in which R2 and R8 are hydrogen, R1 and R10 are methylene, and R9 is an alkenyl, and appendent radicals y and z are zero. Examples of preferred polycarbosilane compounds include poly-dihydridocarbosilane, polyallylhydridocarbosilane, and random copolymers of polydihydridocarbosilane and polyallylhydridocarbosilane. The instant polycarbosilane adhesion promotor compounds can be prepared from well known prior art processes or provided by manufacturers of polycarbosilane compositions.
Specific embodiments of the new and improved polycarbosilane/poly(arylene ether) coating compositions exhibiting superior adhesion to electronic surfaces within the scope of the present invention are provided by those compositions comprising:
a) 100 parts by weight of a polymer compositition selected from the group of poly(arylene ether) homopolymers, block or random copolymers, and polymer blends consisting essentially of: (i) a copolymer of (a) fluorene bisphenol, (b) bis (4-fluorophenyl)ethyne and (c) 4,4xe2x80x2-difluorobenzophenone in a 2:1:1 monomer ratio; (ii) a homopolymer of (a) fluorene bisphenol, and (b) 4-fluoro-3xe2x80x2-(fluorobenzoyl) tolane in a 1:1 monomer ratio; (iii) a homopolymer of (a) fluorene bisphenol, and (b) bis (4-fluorophenyl)ethyne in a 1:1 monomer ratio: and (iv) a homopolymer of (a) fluorene bisphenol and (b) 4,4xe2x80x2-difluorobenzophenone in a 1:1 monomer ratio; and
b) from about 0.5 to 20 parts by weight of an adhesion promoter composition comprising at least one polycarbosilane of the formula: 
xe2x80x83in which:
R1 independently represents a substituted or unsubstituted alkylene, cycloalkylene, or arylene group;
R2 is a hydrogen atom or an organic group; and
x is an average number from about 10 to 15,000.
The new and improved polycarbosilane adhesion promoters and the adhesion enhanced polycarbosilane/poly(arylene ether) coating compositions are efficient and inexpensive to produce and use than prior art materials and exhibit very satisfactory adhesion to the surfaces of electronic devices.